A variety of systems are known for characterizing a cornea, and using information from the characterization to model an ophthalmic lens. See for example U.S. Pat. Nos. 6,413,276; 6,511,180; 6,626,535; and 7,241,311
A difficulty with known systems for characterizing the cornea is that properties of the human cornea can be affected by the amount of water present at the time of measurement. Thus, for example, an ophthalmic lens designed for a patient, where the patient's cornea was characterized when the patient had a dry eye condition, may not be suitable for the patient when the patient's eye is adequately hydrated.
Another problem with conventional systems is the internal structure of the cornea usually is not considered. It is believed that the focusing effect of the cornea is achieved by the anterior surface of the cornea, the posterior surface of the cornea, and the interior structure of the cornea, each contributing about 80%, 10%, and 10%, respectively. This failure to consider the internal structure of the cornea, and in some instances failure to consider the shape of the posterior surface of the cornea, can result in a lens that provides unsatisfactory vision.
Accordingly, there is a need for an improved system for characterizing a cornea for the purpose of obtaining ophthalmic lenses for placement in the human eye. It is also desirable that the system permit analysis of effectiveness of a placed lens in focusing light on the retina.
The invention also includes a system for determining the clarity of vision of a patient to ascertain the effectiveness of an implanted lens or other ophthalmic modification provided to a patient. According to this method, the eye of the patient is illuminated with a scanning light of a wavelength that generates fluorescent light at the retina and clarity of the image generated by the fluorescent light is detected such as with a photodetector. Fluorescent light is generated by proteins in the pigment epithelial cells of the retina as well as photoreceptors of the retina. Then the path length of the scanning light is adjusted to increase the clarity of the image generated by the fluorescent light. Typically the scanning light has a wavelength of from 750 to about 800 nm, and preferably about 780 nm.